It is conventionally well known that sensitizing dyes are added to silver halide emulsions in the preparation of silver halide light-sensitive materials to enlarge the sensitive wavelength regions of the silver halide emulsions, thus optically sensitizing the silver halide emulsions.
Many compounds which can be used as spectral sensitizing dyes for this purpose are conventionally known. Examples of these compounds include cyanine dyes, merocyanine dyes and xanthene dyes described in T. H. James, The Theory of the Photographic Process, third edition, pages 198-228 (Macmillan, N.Y., 1966).
When these sensitizing dyes are applied to the silver halide emulsions, the dyes not only can enlarge the sensitive wavelength regions of the silver halide emulsions, but also must meet the following requirements.
(1) Spectral sensitization region is proper. PA1 (2) Sensitizing efficiency is high and sufficiently high sensitivity can be obtained. PA1 (3) Fogging is not caused. PA1 (4) The variation of sensitivity caused by a change in temperature during exposure is little. PA1 (5) The dyes do not have an adverse interaction with other additives such as stabilizers, anti-fogging agents, coating aids, color formers, etc. PA1 (6) A change in sensitivity is not caused when silver halide emulsions containing the sensitizing dyes are stored. A change in sensitivity is not caused particularly when the emulsions containing the sensitizing dyes are stored under high temperature and humidity conditions. PA1 (7) Color turbidity (color mixing) is not caused after development by diffusing sensitizing dyes added in other light-sensitive layers. PA1 (a) F. M. Hamer, Heterocyclic Compounds--Cyanine Dyes and Related Compounds--(John Wiley & Sons, New York, London, 1964). PA1 (b) D. M. Sturmer, Heterocyclic Compounds--Special Topics in Heterocyclic Chemistry--, Chapter 8, Paragraph 4, pages 482-515 (John Wiley & Sons, New York, London, 1977). PA1 (c) Zh. Org. Khim., Vol. 17, No. 1, pages 167-169 (1981), Vol. 15, No. 2, pages 400-407 (1979), Vol. 14, No. 10, pages 2214-2221 (1978), Vol. 13, No. 11, pages 2440-2443 (1977), Vol. 19, No. 10, pages 2134-2142 (1983); Ukr. Khim. Zh., Vol. 40, No. 6, pages 625-629 (1974); Khim. Geterotski, Soedin., No. 2, pages 175-178, Russian Patents 420643 and 341823, JP-A-59-217761 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), U.S. Pat. Nos. 4,334,000, 3,671,648, 3,623,881 and 3,573,921, European Patents 288261A1, 102781A2 and 102781A2 and JP-B-49-46930 (the term "JP-B" as used herein means an "examined Japanese patent publication").
The above-described conditions are important factors in the preparation of the silver halide emulsions of silver halide color photographic materials.
Many attempts have been made to prevent a lowering in sensitivity from being caused during the preservation of raw samples. However, a lowering in sensitivity cannot be prevented to the desired level.
Particularly, when polymethine dyes having an oxidation potential of 0.60 (V.sub.vs SCE) or lower are used as sensitizing dyes, a lowering in sensitivity during the preparation of raw samples is large and a sufficient performance cannot be obtained.